Quantitative analysis of the a.c. susceptibility of core-shell nanoparticles

摘要

Magnetite (Fe_3O_4) and silica-coated magnetite (Fe_3O_4@SiO_2) nanoparticles (NPs) were synthesized and characterized by scanning and transmission electron microscopy and by a.c. susceptibility measurements as a function of the frequency both at room temperature and 80 K. A new mathematical approach based on the explicit coexistence (at room temperature) of Brownian and Néel contributions is proposed: the magnetic data were quantitatively analyzed following this approach and the results well agree with microscopic data. This mathematical procedure allows the achievement of the complete size distribution of coated magnetic NPs in solution as well as the real dimension of the magnetic nuclei.